1. Field of the Invention
The present invention relates to a power module incorporating means for cooling its power devices.
2. Background Art
Power devices such as IGBTs (Insulated Gate Bipolar Transistors) and power MOSFETs have been widely used in industrial and household appliances, etc., since they are suitable for use in high voltage and high current applications. Because these power devices are used to control a large current, the electrical paths between the devices and external components preferably have low resistance. Further, since power devices generate heat, the power module is preferably constructed to have low thermal resistance to quickly dissipate the heat generated by the power devices out of the module.
Japanese Laid-Open Patent Publication No. 2007-281274 discloses a construction in which power devices are sandwiched between block-shaped upper and lower leads to reduce the electrical resistance of the power module.
Other prior art includes Japanese Laid-Open Patent Publications Nos. 2008-124430 and 2001-230582.
FIG. 7 is a diagram illustrating the construction of a typical power module. In this power module, an IGBT 602 and a diode 604 are mounted on the top surface of a ceramic 608 by solder 612, as shown in FIG. 7. The ceramic 608 serves as an insulating substrate and has a conductive pattern formed on the top surface. Wires 606 are connected between electrodes of the IGBT 602 and the diode 604 and terminals 618. The terminals 618 are mounted in a resin case 601 and used to connect the IGBT 602, etc. to an external component. On the other hand, a metal plate called a “base plate 614” is coupled to the bottom surface of the ceramic 608 by solder 610. A cover 616 is fitted in the opening of the resin case 601, thereby completing the manufacture of the power module 600.
Some of the heat generated in the power module 600 can be dissipated by radiation from its base plate 614. However, it is common that the base plate 614 is coupled to a radiating fin structure 702 with cooling grease 704 therebetween in order to sufficiently dissipate heat from and cool the power module 600, as indicated by the arrow in FIG. 7.
However, the configuration of the power module with the radiating fin structure 702 as shown in FIG. 7 does not allow for a reduction in the electrical resistance and a further improvement in the heat dissipation characteristics of the power module. Specifically, the wires 606 and the conductive pattern on the ceramic 608, which are used as electrical paths, prevent reduction of the electrical resistance of the power module. Further, the heat generated by the IGBT 602, etc. is dissipated through the path formed by the ceramic 608, the solder 610, the base plate 614, the grease 704, and the radiating fin structure 702. That is, this heat dissipation path has high thermal resistance, preventing the application of full power to the power devices such as the IGBT.
The configuration disclosed in the above Japanese Laid-Open Patent Publication No. 2007-281274 allows for a reduction in the electrical resistance of the power module, but does not have sufficient heat dissipation characteristics. Furthermore, the leads are not sufficiently insulated, since large portions of them are exposed at the resin surfaces.